Set and mostly taking place in New York City, Kabhi Alvida Naa Kehna explores themes of adultery and extramarital affairs. Kabhi Alvida Naa Kehna was promoted with the tag-line, "A Love.... That Broke All Relationships". It was a success internationally especially in the United States. It became the highest grossing Indian film of all time overseas at the time of its release. The film was screened in over 1,200 cinemas worldwide,[4] grossing a worldwide total of ₹1.13 billion (US$17 million).[5]

Maya (Rani Mukerji) is an orphan who is to marry her closest childhood friend Rishi Talwar (Abhishek Bachchan). The two have been raised by Rishi's fun-loving father Samarjeet a.k.a. Sam (Amitabh Bachchan). Dev Saran (Shah Rukh Khan) is a successful soccer player in the United States. He lives in New York with his wife Rhea (Preity Zinta), a fashion magazine editor, his young son Arjun (Ahsaas Channa) and his mother Kamaljeet a.k.a. Kamal (Kirron Kher). Dev encounters Maya moments before she is to marry Rishi, and the two have a deep conversation about love, life and happiness. Although Dev and Maya are strangers, they connect instantly. When Dev bids Maya goodbye, she tells him they should never say goodbye because it kills the possibility of meeting again. Moments after they part, Dev is hit by a car and permanently injures his leg; as a result, he is no longer able to play soccer.

Four years later, Dev is now extremely bitter because of his inability to play soccer and because of Rhea's successful career which makes him feel inferior to her. Maya too is in a similar situation. She has found that she is infertile and does not feel any love towards Rishi because she believes he is selfish. The two couples meet and become friends. When Dev and Maya witness Sam and Kamal embracing at a flower shop, they confront them about it. Sam and Kamal explain that both having lost their spouses, they understand each other better than the others as both of them are in similar situations and have decided to help one another through their loneliness by means of friendship. Dev and Maya notice each other's marriages failing miserably, and taking into account what Sam and Kamal said, they decide that they need to help each other save their marriages. They meet every day for coffee and discuss their situations and advise each other in understanding their respective spouses better. Eventually, Dev and Maya decide to take a break from the stress of their respective relationships and spend some quality time together. In doing so, they find themselves drawn to one another.

Dev and Maya arrange a dinner for their respective spouses on the occasion of their wedding anniversaries so as to salvage their respective marriages to some extent. After returning home from the dinner, both couples have an argument. Rhea accuses Dev of being jealous of her professional success and also makes Dev realize his failure in being a good father to their son. Rishi expresses frustration at the lack of affection that Maya has shown towards him and he resents Maya's inability to have children. Upset and misty-eyed, Maya arrives at the train station and finds Dev, who after a confrontation finally confesses that he has fallen in love with Maya, and so has she.

Sam and Kamal, after noticing the failing marriages of their respective children, set up Rhea and Rishi into talking to each other about their marriages. Rhea and Rishi realize they need to stop arguing with their spouses and reach out to them. For a while, both marriages seem to be fine; however, Dev and Maya begin an affair, as they are happier with each other than with their respective spouses. The two couples attend a ballet show, where Dev and Maya try making each other jealous by showing affection to their partners. The next day, they realize that they have been playing with their spouses' feelings but nevertheless give in to their love and cross the forbidden limit by sleeping together.

Sam invites the Sarans to dinner to celebrate Kamal's birthday. Here, after a conversation on love, marriage and fidelity, Dev 'jokingly' admits he loves Maya; Sam is the only one who realizes that Dev was being serious. The next day, Dev and Maya are caught in an embrace outside the train station by Sam and Kamal. Sam has a heart attack; on his deathbed, he advises Maya to leave Rishi, as neither of them is happy in the relationship and never will be. He also advises her that by being together in a loveless marriage, she was depriving Rishi and herself of true love and happiness in life. After Sam's death, Dev and Maya decide they must end their relationship and go back to their respective spouses, but first they must tell them the truth first about their extramarital affair; as lying to their spouses would never give them peace and happiness. Shocked and heart-broken, Rhea and Rishi decide they have had enough and divorce their spouses. Dev and Maya lie to each other and say that they have managed to sort things out with their spouses, believing they'll never meet again.

Three years have passed since their last encounter with each other. Dev and Maya now live alone miserably and have not seen each other. Rishi visits Maya and says that he has fallen in love again and is remarrying, and wants Maya to be his best man, to which she agrees. Rhea, having also been invited, arrives at Rishi's wedding with her boss Jay (Arjun Rampal in a cameo), whom she is now dating. Rhea learns that Rishi and Maya are divorced – Rishi learns the same about Dev and Rhea. Rhea, after confronting Maya tells her that she had left Dev as soon as she came to know of his affair with her and that she had forgiven Maya. Maya is encouraged by Rishi and Rhea to stop Dev, who is leaving for Toronto by train, as they have both moved on and believe Maya should also find her true love and happiness. At the train station, Dev sees Maya but tries to avoid her, believing she is still with Rishi. However, Maya finds him just as the train leaves. Maya, disappointed and heart-broken, leaves the train station. Dev, having seen Maya's teary eyes, pulls the emergency stop and arrives back at the station. He makes it back before Maya leaves the train station. He calls out to Maya and both of them are glad to see each other after three years. He learns that Maya has also been divorced and was living alone in these three years. They finally find happiness with their true love and decide to start a new life together. At the end, Dev narrates that love should be the only foundation of marriage but it shouldn't be at the expense of hurting others.

Kajol was initially offered the role of Maya Talwar. When she refused, due to her prior commitments with Yash Raj Films's Fanaa, the role was passed on to her cousin Rani Mukherji, who was supposed to play Preity Zinta's part. However, Kajol made a guest appearance in the song "Rock 'N' Roll Soniye". Ritesh Deshmukh also had a guest appearance, but his scene was cut during the editing process.

Kabhi Alvida Naa Kehna is set in New York City, while many of the scenes were filmed nearby in East Hartford and New Haven in Connecticut. The soccer game scene was filmed at Rentschler Field, the home of the UConn Huskies football team. In several scenes, a light 'UConn' can be seen on the field. The majority of the Grand Central Station scenes were filmed at New Haven's Union Station and Philadelphia's 30th Street Station. It was filmed over a 90-day shooting period in the USA but a few scenes were shot on four large sets in Mumbai studios.[7]

This is the second time that lyricist Javed Akhtar and the composers Shankar-Ehsaan-Loy have teamed up for a Dharma production. The title song Kabhi Alvida Naa Kehna rendered by Sonu Nigam and Alka Yagnik is a tear jerker. Mitwa, an evocative sufi rock ballad, marked the introduction of Pakistani singer Shafqat Amanat Ali into the Bollywood scene. Rock 'N' Roll Soniye, picturized on Amitabh, Abhishek and Preity is a 60's Rock 'N' Roll track, sung by Shankar Mahadevan, Shaan and Mahalakshmi Iyer. Then follows Tumhi Dekho Naa, a soft and romantic ballad, which again is sung by the Sonu Nigam - Alka Yagnik duo, is picturised on Shahrukh and Rani. Where's The Party Tonight? by Shaan, Vasundhara Das, Loy and Shankar Mahadevan is the club song picturized on Abhishek and Preity. Farewell Trance is the trance version of the title track, which is a rarity in Bollywood. The album also has a remix - Mitwa - Revisted.[8]

The trio took care to not make the album sound repetitive, especially since the overall genre of the soundtrack is similar to that of their previous chartbuster Kal Ho Naa Ho[9] (2003).

The music of Kabhi Alvida Naa Kehna was launched in the United Kingdom on 12 June 2006 and was officially released in India on 16 June 2006 along with a grand music launch at the IIFA Awards function in Dubai.[10]

Though there were a few negative buzz around earlier at London where the music released,[11] the overall reaction to the album was positive from all the mainstream critics. Joginder Tuteja of Bollywood Hungama dismissed those initial negative reaction, saying "Much before the official release of the music album of KANK, rumor brigade has been having a field day in pulling down the album. Well, that's not something new as with every biggie comes its share of detractors. But on hearing the songs for yourself, you realize that is it NOTHING, but a rumor! The album is yet another fine product from the team that delivers the kind of path-breaking music expected from it."[13] Sukanya Verma of Rediff called the album " a treat for the melody-starved.".[12]

The album opened at #1 and retained the top position in the music charts for ten straight weeks, despite facing tough competition from musical hits like Fanaa, Krrish and Gangster.[14] According to the figures from BoxOffice India, the album sold over 1,900,000 copies in India[15] making it the second best selling album of the year, marginally behind Dhoom 2.

On its release, the film received positive reviews from critics worldwide.

Critic Taran Adarsh described the subject matter as a delicate one which could have easily been disastrous and praised the way in which director Karan Johar boldly constructed the film, citing it as his finest work to date.[16] Adarsh approved in particular of the script and the devices the director incorporated to contrast emotions between scenes, remarking that, "the screenplay balances the two extremes; light moments and dollops of emotions with amazing ease".[16] The individual cast performances were also praised by Adarsh, who commented on the effectiveness of the casting and the interaction of the actors.[16]

Rajeev Masand gave the film 4 out of 5 stars praising the screenplay and Johar's direction, saying "Few writers have such solid control over their screenplay as Karan Johar does. Few understand the intricacies of narrative as well as he does. Johar goes from highs to lows, from plateaus to peaks with the ease of a pro. He knows exactly how to turn a seemingly ordinary scene into something special with just that one line of dialogue, or that hint of background music."[17]

Derek Elley of Variety also praised the diversity of emotions displayed by the cast, remarking that, "scripter Shibani Bathija never lets her characters inhabit a secure emotional place for very long, and impediments to happiness come from their own weaknesses rather than social constraints or plot-generated misunderstandings".[18] Elley noted Amitabh Bachchan's performance as an ageing lothario and praised Preity Zinta as "stepping far beyond her makeup".[18]

Raja Sen of rediff.com was particularly critical of the film, also expressing dissatisfaction with its length. He remarked, "I feel older. A showing of Karan Johar's mammoth 22-reel Kabhi Alvida Naa Kehna has left me unbelievably exhausted. I walked out of the hall feeling my cheeks for stubble, wondering if my clothes are suddenly dated and my hair's turned grey. I've lost a sizeable chunk of my life, and you will too".[19] Unlike other critics, he identified flaws in the script and criticised the strength of characters saying "The characters are cardboard, the setting is glitzy, the songs are tiresome, and the story oscillates between high melodrama and slapstick hilarity, going nowhere. Rarely has a weak script relied so completely on pretty people with big names to carry every line through".[19]

In the United States, the film received a number of positive reviews.

Critics such as Neil Genzlinger of the New York Times emphasised the larger-than-life nature of the film, remarking that, "It is full of big Bollywood stars and outsized everything: the rainstorms are a little rainier than real life; the wind machines are cranked up an extra notch; the close-ups get closer and linger longer than usual; the coincidences that drive the plot are a little more numerous and unlikely than normal screenwriting allows".[20] He praised the humour in the script and the director's comic timing in certain scenes such as the children's soccer match, the bed store, and at the ballet show.[20]

Kabhi Alvida Naa Kehna saw a record opening at many cities in India and generated ₹ 600 million in the first week itself, although it is currently Johar's lowest-grossing film according to net collections, even if unadjusted for inflation. It emerged the highest grosser worldwide for an Indian film, surpassing Kabhi Khushi Kabhie Gham's five-year-old record.[4] The film is currently the seventh highest grosser overseas with a total gross of $10 million.[21]

It opened strongly in the United States and the United Kingdom with first weekend grosses of $1.3 million in the U.S and $1.4 million (£750,000) in the UK[22]

In total Kabhi Alvida Naa Kehna collected US$3,275,444 in the United States[23] while in UK it netted over £5,079,688.00. In the US, one factor contributing to its success was the fact it debuted in 64 theatres, unusually high for a Bollywood film in cities with lower Indian populations such as Miami, Tampa, and Raleigh as well.[citation needed]